The present invention relates to plate-like hematite particles, an iron oxide pigment comprising the same and showing a golden color, and a process for producing the same. Such an iron oxide pigment is chiefly used as a coloring material for paints, rubber compositions, resin compositions, printing inks, cosmetics and the like showing a golden color.
Further, the present invention relates to a paint, a rubber composition or a resin composition containing the iron oxide pigment and showing a golden color with metallic luster. Such a paint, rubber composition and resin composition are mainly used as materials for electric appliances, daily necessaries such as tableware, building materials, containers and accessories such as buttons.
Also, the present invention relates to a method for drawing a three dimensional picture (stereograph). Such a method is applied to the fields of the manufacture of the electric appliances, the daily necessaries, the building materials, the containers and the accessories.
Hematite (colcothar) particles which are typical of iron oxide pigments, show a red color, so that they are widely used as a red color pigment for producing paints, printing inks and cosmetics. Plate-like hematite particles show a black purple color and are used as a black purple pigment. Since the plate-like hematite particles are oriented in a superposed state, they are excellent in the coating property, so that they are also used as an anti-corrosive pigment.
Generally, since iron oxide pigments are oxides, they have a high resistance to the acid in the vehicle during producing a paint or the like, and an excellent resistance to environment pollution or the like.
However, goods have recently been required to have not only functional qualities but also sensuous quality characteristics. In particular, as to colors, a golden color with a metallic luster which make a high quality impression has been strongly demanded.
A golden color with a metallic luster is conventionally economically obtained by blending a brass powder, a powder alloy of brass and zinc, or a mixed powder of a brass powder and a zinc powder into a vehicle.
However, if it is produced by the conventional method, since the pigment is a metal powder, the resistance to the acid in the vehicle is low and the resistance to environment pollution or the like is also low, so that the stability thereof is insufficient.
On the other hand, although an iron oxide pigment is excellent in the stability, as described above, it is a red coloring pigment and no iron oxide pigment showing a golden color has yet been produced.
For example, processes for producing an iron oxide pigment showing a red color have been proposed in Japanese Patent Application Laid Open (KOKAI) No. 61-174120 (1986) which corresponds to U.S. Pat. No. 4,676,838 and Japanese Patent Application Laid Open (KOKAI) No. 55-104923 (1980) which corresponds to U.S. Pat. No. 4,404,254 .
U.S. Pat. No. 4,676,838 discloses lamellar pigments consisting of .alpha.-iron oxide with an Fe.sub.2 O.sub.3 content of at least 88%, an average particle diameter of from 0.5 to 20 .mu.m, an average ratio of diameter to thickness of from 20 to 100, and an almost normally distributed particle size distribution, the relative standard deviation of which, based on the average value of the normal distribution, is less than 0.3, and showing a copper-colored to red color; and a process of production of an .alpha.-iron oxide pigments by the hydrothermal treatment of a trivalent iron-containing solution or suspension, comprising adding to the solution or suspension prior to the hydrothermal treatment active .alpha.-iron oxide seeds with lamellar or disc-like crystal form and a specific surface of at least 10 m.sup.2 /g.
U.S. Pat. No. 4,404,254 discloses hexagonal, lamellar iron oxide particles substantially homogeneously about 0.1 to 12% by weight of at least one oxide of an element of the IVth, Vth or VIth Main and Secondary Groups and of the IInd Secondary Group of the Periodic System of elements, and showing a bluish red to yellowish red color; and a process for production of hexagonal, lamellar iron oxide particles which is characterized in that compounds of at least one of the elements of the IVth, Vth and/or VIth Main and/or Secondary Group and/or of the IInd Secondary Group of the Periodic System of the elements are present during the growth of the iron oxide particles or of identically shaped precursor crystal particles in the hydrothermal production.
Accordingly, the establishment of the process for producing an iron oxide pigment which shows a golden color has been strongly demanded.
On the other hand, paints are generally obtained by mixing coloring pigments as a coloring material, which show a color and luster, into paint base materials such as resin, solvents, body color pigments and if necessary, drying accelerators, surfactants, auxiliary agents and the like, from the viewpoints of vision and beauty.
Also, rubber or resin compositions are obtained by mixing coloring pigments as a coloring material, which show a color and luster, into rubber or resin composition base materials such as various kinds of rubber or synthetic resins and if necessary, plasticizers, stabilizers such as antioxidants, ultraviolet absorbers and the like, from the viewpoints of vision and beauty.
In general, paints, rubber or resin compositions showing a golden color with metallic luster can be economically obtained by mixing a brass powder, a powder alloy of brass and zinc or a powder mixture of brass powder and zinc powder with paint base materials, rubber composition base materials or resin composition base materials. However, in these paints, rubber or resin compositions, the resistance to the acid in the paint base materials, the rubber composition base materials or the resin composition base materials used during the formation thereof is low and the resistance to environment pollution is also low. Therefore, it has been strongly demanded to provide paints, rubber or resin compositions having excellent resistance to the acid therein and to environmental pollution.
Recently improvements in culture and life have required in not only functional qualities but also quality characteristics of goods in view of sense and interest. Appearances in which three-dimensional pictures are formed, are particularly important factors which increase a feel of high grade and depth to determine the value as commercial products.
Three-dimensional pictures can be formed by, for example, a method of forming uneven patterns on the surfaces of molded products, as disclosed in Japanese Patent Publication No. 62-16832 (1987), a method of spraying or printing paints or ink having desired compositions so that color differences and gloss differences can be produced, or a method of employing jointly such methods.
Although there is now a greater demand for the formation of three-dimensional pictures (images), in the above-described known method of forming uneven patterns on the surfaces of molded products, since three-dimensional pictures are formed by the depth of unevenness, three-dimensional pictures cannot be satisfactorily obtained because of the limit of the depth itself, and pictures of the complicated forms cannot be easily shown only by using unevenness.
Further, in the above-described known method of spraying or printing paints or ink, it is difficult to produce satisfactory color differences or gloss differences because it is necessary to use various types of paints or ink having various colors and various degrees of gloss, and to repeat selective coloring processes in accordance with the form patterns. In addition, although a three-dimensional pictures can be formed by stepwisely changing the degree of a depth of unevenness or the degrees of a color difference and a gloss difference, since this method requires a complicated steps, such method thus exhibits poor workability and poor productivity, and is an industrial and economical method.
As a result of the present inventors' studies for dissolving such problems, it has been found that by autoclaving an alkaline suspension of iron (III) oxide hydroxide particles, FeO.sub.x.Fe.sub.2 O.sub.3 (0.ltoreq..times..ltoreq.1) particles or a ferric salt, a pH of the alkaline suspension being not less than 9, 0.1 to 15.0 mol of water-soluble salt based on 1 mol of Fe being added to the alkaline suspension and an Si-containing compound being added to the alkaline suspension so as to contain 1.5 to 20.0 mol. % of Si based on the total amount of Fe in the alkaline suspension, plate-like hematite particles having an average particle diameter of 0.5 to 5.0 .mu.m, a lamellar thickness of 50.ANG. to 500.ANG. and a plate ratio (the ratio of the average particle diameter to the lamellar thickness) of 50:1 to 500:1 and showing a golden color have been obtained. The present invention has been achieved on the basis of this finding.